1. Field of the Invention
The present invention relates to a movable stand employing a parallel crank arm mechanism, and more particularly to such a movable stand in which one of the parallel arm members is shaped into a tubular configuration in order to conceal therein the other parallel arm member.
2. Description of the Prior Art
Movable stands employing a parallel crank arm mechanism have been conventionally utilized for carrying head units of devices such as lamps or book holders to be installed adjacent desks, beds or the like places. Such movable stands are disclosed in U.S. Pat. Nos. 4,080,530, 4,160,536, 4,165,530 and 4,213,172, in each of which a pair of arm members forms a parallel crank in combination with a pair of brackets pivotally connected to both ends thereof, the parallel crank additionally including a spring which provides a counterbalancing effect upon the parallel crank. Any of these prior movable stands, however, employs a parallel crank of a primitive configuration such that the very structure of the parallelogram is explicitly exposed presenting a definite gap between two parallel arm members. A parallel crank having such a primitive configuration inherently accompanies the character that the gap width varies as the parallel crank swings. The gap width practically reaches its maximum where the parallel crank arm extends in the vertical direction and is gradually reduced with increase of reclining angle to its minimum where the parallel crank extends in the horizontal direction. Due to this variable nature in the width of the exposed gap during the swing motion of the parallel crank, there is a constant danger of pinching a user's fingers between the two parallel arm members when he or she is trying to adjust the angular position of the movable stand from an upright position to a horizontal position with the attendant narrowing of the gap. In addition to this fatal drawback, the primitive configuration of the parallel crank arm with the exposed gap may, in most instances, give a clumsy appearance. Furthermore, this unfavorable factor is emphasized when the gap between the two arm members is selected to be greater for preventing the danger of finger entrapment.